1. Field
The present invention relates to translating lower frequency signals to higher frequency signals and higher frequency signals to lower frequency signals. More specifically, the present invention relates to an apparatus and method for up converting microwave signals to millimeter wave signals and down converting millimeter wave signals to microwave signals for use in such applications as a radar transceiver.
2. Description of Related Art
Communication and radar systems operating with signals in the microwave frequency band (3–30 GHz) are well-known in the art. Systems operating at higher frequencies are also known in the art. Such systems are often implemented using one or more transceivers that both transmit and receive the signals. Operating at higher frequencies is desirable because the size of the antennas used with the transceiver scale inversely with the operational frequency. As a result, higher frequencies result in smaller antennas while still realizing the same gain. This is important for applications that require a compact transceiver, such as in commercial vehicular applications. Higher frequencies also provide better Doppler resolution thus improving the quality of data transmitted and received.
Millimeter wave transceivers are typically designed with frequency multiplier stages immediately following the voltage controlled oscillator (VCO). As a result, all the components of the transceiver (mixers, amplifiers, etc.) must be operable at the higher multiplied frequency which increases the cost of the components. Furthermore, typical frequency multiplier stages comprise expensive active components that require complicated circuitry and introduce undesirable noise into the system.
FIG. 1 shows a prior art automobile radar system 200 for operation within the millimeter wave frequency band. The system 200 comprises an oscillator 210 operating at 19–19.25 GHz followed by a first amplifier 212. The amplified signal is then doubled in frequency by a first frequency multiplier 220. The doubled frequency signal is then amplified by a second amplifier 222. A second multiplier 230 then doubles the frequency of the signal to be at 76–77 GHz. A Microwave Monolithic Integrated Circuit (MMIC) switch 240 is then used to switch the signal among multiple antenna elements 250 for transmission. A radar return signal is received by the antenna elements 250 and is directed to a mixer 260 by the MMIC switch 240. Since the transmitted signal is at 76–77 GHz, the mixer 260 uses a Local Oscillator signal at the same frequency to downconvert the radar return signal to an Intermediate Frequency (IF) signal. A low pass filter 262 is used to filter out signals at frequencies higher than that of the IF signal.
The system depicted in FIG. 1 illustrates some of the problems seen with transceiver systems known in the art. As can be seen from FIG. 1, multiple frequency multiplier stages are used after the voltage controlled oscillator to translate the oscillator signal at a microwave frequency to a signal in the millimeter wave frequency band. These components can impose considerable cost, size and power constraints on the system compared to components that need only operate at lower frequencies. Further, down conversion of the radar return is achieved with a mixer operating in the millimeter wave frequency band. Again, such components operating in the millimeter wave frequency band may cost considerably more, be larger than, and/or require more power than components that need only operate at lower frequencies.
Therefore, there is a need for an apparatus and method for sending and receiving signals at higher frequencies that can utilize components for lower frequency applications, while still providing the benefits of operation at higher frequencies.